Isolation and Identification Methods for Slackia Exigua and Investigation of the Relationship between this Organism and Peri-Implantitis

In the genus Slackia, Slackia exigua (formerly Eubacterium exiguum) is isolated from the human oral cavity. A relationship was recently reported between S. exigua and periodontal disease, including chronic periodontitis and peri-implantitis. A suitable selective medium for the isolation of S. exigua is needed in order to assess the veritable prevalence of this organism in various lesions of the oral cavity. The purpose of the present study was to develop selective media for the isolation of S. exigua and investigate whether the monitoring of S. exigua levels is useful as a clinical indicator for the diagnosis of peri-implantitis. In order to examine the bacterium population in the oral cavity, a novel selective medium (SEXSM) was herein developed for the isolation of S. exigua. SEXSM consists of tryptic soy agar, yeast extract, hemin, Vitamin K1, L-cysteine, sheep blood, 2-phenylethanol, trimethoprim, nalidixic acid, and polymyxin B. The average growth recovery of S. exigua on SEXSM was 98.3% that on CDC blood agar. The growth of other representative oral bacteria, i.e., the genera Streptococcus, Actinomyces, Neisseria, Corynebacterium, Veillonella, Fusobacterium, and Rothia, was strongly inhibited on the selective medium. PCR primers were designed based on partial sequences of the 16S rDNA genes of S. exigua. These primers reacted with S. exigua, but not with other representative oral bacteria. These results indicate that these primers are useful for identifying S. exigua. The proportion of S. exigua in Gingival Crevicular Fluids (GCF) collected from periodontally Healthy with Implants (HI) and Peri-Implantitis (PI) groups was examined. Colonies on SEXSM were subcultured for confirmation by a PCR analysis using the primers designed in the present study. The growth recoveries of S. exigua strains on SEXSM were very satisfactory. S. exigua in GCFs of the HI and PI groups were detected at 0.002%, and 1.7% to the total bacteria number, respectively. The selective medium, designated SEXSM, and a PCR method using the primers designed in the present study were useful for the isolation and identification of S. exigua. Moreover, the monitoring of S. exigua levels was useful as a clinical indicator for the diagnosis of periimplantitis.